Electroplating of zinc and electrolyte therefor



Patented Oct. 3, 1950 Allan E, 'ChesterjHighland Park, and Frederick;

" F. Reisinger, Waukegan, Ill., assignors'to P o'or f & Company, Chicago, Ill.,

' Delaware N oDrawing. Application March 6, Serial No. 525,324

' ms o1. 204-55) This invention relates to a new andimproved ;method of electroplating zinc {roman alkaline .-zinc .cyanidebath, and to a new and improved .electrolyte therefor.

v; One ofthe objects of the invention'is to provide a'new and improved type of electrolyte for electroplating zinc from alkaline cyanide baths.

Aijfurther object of the invention is the pro- --visionof new and useful electrolyte'baths which do not form precipitates and do not tend to coagulate' on standingEover long periods of time.

Another object of the'invention is to provide a new and improved method of electroplating zinc'wherein electroplated articles having a very bright finish are produced.

)An additional object of the invention is' to provide a new and improved method of incorporating into alkaline zinc electrolytes organic substances (capable of forming complex metallo organic compounds with the metallic ions present in the bath.

Another object of the invention is to provide a new and improved methodofaadding to alkaline zinc cyanide baths for specific'purposes certain types ,of compounds or derivatives thereof in a form-,in which the compounds or theirde rivatives remain in solution in the bath and'can be added in relatively larger proportions than has heretofore been practical with the compounds per se; Other objectswill appear hereinafter. v

These objects are accomplished in accordance with this invention by incorporating into alkaline zinc cyanide electrolyte baths-reaction products of;a;gelatin and an aldonic acid, preferablythe reaction product of. gelatin with gluconic acid. When zinc is electroplated from such baths on the customary base materials, the resultant electroplated products have a greatly improved brightness offinish. Especially good results are obtained vvith current densities. up to 30-40 amperes per squarefootalthough bright finishes can be obtainedat higher current densities withoutburning.

One f the important features of the invention is the great stability of the electrolyte baths and of the aldonic acid-gelatin derivatives which are added to these baths. The baths maybe used over long periods of time at temperatures the,:bath a, complex metallo organic compou a corporation of distinguished from gelatin per se added to a similar type of electrolyte floats around in masses or blobs,

For the purpose of the inventio 1 V erable to addza'n excess of the aldonic the bath as apart of the solution produce the treatment of a gelatin with the. aldo'rii v The excessfof the aldoniciacid, as pre ,ously indicated, forms with the zinc. ions)?" and in the practice of theinventioniit ha found that the electrolyte -bat'hsusedha U A high initial cathode efficiency, which i appar 1y due to the presence of thecomplex .metal ions of the aldonic acid.

In the preparation-of composition in electroplating zinc in; alkalinercyam a further feature of the ,invention;;;i J dition of furfural to the gelatinga-ldom, a d derivative. Furfural formswith thesolutrornpf this derivative a clear stable solution; ofa. what deeper yellow color than that pf th atin-aldonic, acid derivative. Ordinarily, 5 very diflicult-to add substantial amounts-of. :furs fural to electroplatingbaths, but. by adding-the furfural to the gelatin-aldonic acidi' derivativ'e,

'Examplel The gluconic acid-gelatinderivative wasp pared by mixing together 34 grams, of gela; and cc. of 50%,g1uconic acid. The reaction; mixture was digested from -to"1;--ho ur aztga.

forms a gel with the gelatin, andthe: addition of the water with vigorous stirring and. heating converts this gel into a solution. The resultant product is stable and does notg tendrto precipi tate 'or coagulate onistanding. --It is clear and has a yellowish. rcolor. Thistproduc't icani be' added directly toi anzgalkaline zinc'cyanide electroplating bath with excellentaresults.

foot.

Example II Example III This example illustrates the application of the products of Examples I and II and the preparation of alkaline zinc cyanide electrolytes.

An electrolyte was prepared by mixing together the following ingredients:

90-100 grams sodium cyanide 36-40 grams zinc metal (added in the form of zinc oxide) 100-115grams sodium hydroxide and enough water to make 1 liter of solution 2 grams per liter of zinc dust was stirred into the electrolyte and the entire mixture was filtered in order to remove traces of heavy metals.

This electroplating bath when employed in a conventional manner ordinarily produces zinc electroplated articles with a dull gray finish. Upon the addition of either of the products of Examples I or II, however, preferably in amounts corresponding to from 60 to 80 cc. of either of said products per gallon of the above described alkaline zinc cyanide electrolyte, bright finishes are obtained.

In electroplating operations with these electrolytes especially good results with respect to the brightness of the finish are obtained with current densities up to 30-40 aniperes per square At greater current densities bright zinc coatings are still obtained, but in'general the coatings are not quite as bright as those obtained at the lower current densities. The prodnets are especially useful in barrel-plating operations but can be used in other types of operations without burning of the coating even at the higher current densities.

The invention is susceptible to some variation and modification in the manner of its practical application. In general, it is preferable to employ gluconic acid because it is the most cheaply mum concentration of aldonic acid employed is that which will form a gel with the gelatin. As

examples of other aldonic acids which may be used, mention is made of the following: mannonic, arabonic, galactonic, and xylonic. These acids are obtained by the oxidation of the corresponding aldoses and all have alpha and beta lactone forms. The gelatin employed may be any of the ordinary types. of gelatins obtained from animal tissues. in the usual way, by boiling them under pressure with water. The term gelatin is used herein in its ordinary sense, as defined in Hackhs ChemicalDi'ctionary, 1929., page 326.

It will be understood that the electroplating baths; of the present invention maybe employed iordirect current electroplating in the usual manner, and also giveexcellent result$ wh n employed in electroplating zinc from alkaline zinc cyanide electroplating baths using alternating current superimposed upon direct current.

The term cyanide-zinc plating bath, as em-- ployed herein, is used generically to cover any alkaline cyanide plating baths for electroplating zinc, which may or may not contain other substances added for special purposes. Electroplating baths of this type are so well known in the art that further description of them is considered unnecessary. The plating baths of the present invention apparently contain zinc ions in several forms, including complex inorganic ions such as zincate ions due to the presence of the alkali and complex metallo organic ions due to the presence of zinc gluconate.

The method of electroplating herein described provides a new and improved way of obtaining bright zinc finishes. The electroplating baths produced in accordance with the invention are characterized by excellent stability. Furthermore, as previously indicated, the incorporation into the bath of gelatin-aldonic acid derivatives containing excess aldonic acid produces results which cannot be obtained by adding the gelatin alone or the aldonic acid alone. Likewise, the incorporation into the baths of gelatin-aldonic acid-furfural derivatives gives results that are not obtained from the separate components added as such.

The invention is hereby claimed as follows:

1. An aqueous cyanide-zinc plating bath comprising an alkaline cyanide-Zinc electroplating bath and the bath soluble chemically combined reaction product of a gelatin with an aldonic acid.

2. An aqueous alkaline cyanide zinc electroplating bath comprising an aqueous alkaline cyanide solution containin zinc in the form of an aldonate and the water soluble chemically combined reaction product of a gelatin with an aldonic acid.

3. An aqueous cyanide-zinc plating bath com prisin an alkaline cyanide-zinc solution containing the chemically combined bath soluble reaction product of a gelatin, an aldonic acid, and

furfural.

4. An aqueous cyanide-zinc plating bath comprising an alkaline cyanide-zinc electroplating solution and the chemically combined bath soluble reaction product of a gelatin with gluconic acid.

5. An aqueous cyanide-zinc plating bath com- 7 prising an alkaline cyanide-zinc electroplating solution and a solution of the chemically combined reaction product of gelatin, gluconic acid and furfural.

6. An aqueous zinc electroplating bath comprising a major proportion of an alkaline cyanide-zinc solution and a minor proportion of a solution of the chemically combined reaction product of gelatin With an aldonic acid.

'7.'An aqueous zinc electroplating bath comprising a major'proportion of an alkaline cyanide containing complex zinc ions and a minor proportion of a solution of the chemically combined reaction product of gelatin with gluconic acid.

8. An aqueous zinc electroplating bath comprising an alkaline cyanide solution containing complex zinc ions and a solution of the chemically combined reaction product of gelatin and gluconic acid in proportions of about 60 to cc. per gallon of plating bath.

9. An aqueous zinc electroplating bath comprising an alkaline cyanide solution containing complex zinc ions and a solution of the chemically combined reaction product of gelatin, glutonic acid and furfural in proportions of about 60 to 80 cc. per gallon of plating bath.

10. In a process for the electrodeposition of zinc, the step which comprises depositing zinc from an aqueous cyanide-zinc plating-bath in the presence of the chemically combined reaction product of a gelatin and an aldonic acid, said reaction product being bath soluble.

11. In a process for the electrodeposition of zinc, the step which comprises depositing zinc from an aqueous cyanide-zinc. plating bath in the presence of a solution of the chemically combined reaction product of a gelatin, an aldonic acid, and furfural.

12; In a process for the electrodeposition of zinc, the step which comprises depositin zinc from an aqueous cyanide-zinc plating bath in the presence of the chemically combined reaction product of a gelatin and gluconic acid reacted in gel-forming proportions and dissolved in water.

13. In a process for the electrodeposition of zinc, the step comprising depositing zinc from an aqueous cyanide-zinc plating bath in the presence of the chemically combined reaction product of gelatin, furfural, and gluconic acid, said reaction product being bath soluble.

14. In a process for the electrodeposition of zinc from a cyanide-zinc plating bath, the step which comprises depositing zinc from an aqueous cyanide-zinc plating bath containin zinc gluconate and the water soluble chemically combined reaction product of gelatin and gluconic acid.

15. In a process for the electrodeposition of zinc from a cyanide-zinc plating bath, the step 6 which comprises depositing zinc from an aqueous cyanide-zinc plating bath containing zinc gluconate and the water soluble chemically combined reaction product of gelatin, gluconic acid and furfural.

16. The process for electrodepositing zinc from a cyanide-zinc plating bath which comprises depositing zinc from an aqueous cyanide-zinc plating bathcontaining zinc gluconate and a quantity of the Water soluble chemically combined reaction product of gelatin and gluconic acid resulting from the reaction of gelatin with gluconic acid in proportions corresponding to about 34 grams of gelatin and 100 cc. of gluconic acid digested together from one-half hour to one hour at a temperature of from 80 degrees F.

to 120 degrees F. to form a gel followed by the addition of an amount of water sufiicient to dissolve said gel, said quantity corresponding to about cc. to cc. 'of the resultant solution of the gelatin-gluconic acid reaction product in water per gallon of aqueous cyanide-zinc plating bath.

ALLAN E. CHESTER.

FREDERICK F. REISINGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 694,658 Meurant Mar. 4, 1902 1,894,669 Conlin Jan. 17,193 2,196,588 Hull Apr. 9, 1940 2,390,511 Chester et a1 Dec. 11, 1945 2,458,504 Chester et al Jan. 11, 1949 2,461,809 Chester et a1 Feb. 15, 1949 

1. AN AQUEOUS CYANIDE-ZINC PLATING BATH COMPRISING AN ALKALINE CYANIDE-ZINC ELECTROPLATING BATH AND THE BATH SOLUBLE CHEMICALLY COMBINED REACTION PRODUCT OF A GELATIN WITH AN ALDONIC ACID.
 10. IN A PROCESS FOR THE ELECTRODEPOSITION OF ZINC, THE STEP WHICH COMPRISES DEPOSITING ZINC FROM AN AQUEOUS CYANIDE-ZINC PLATING BATH IN THE PRESENCE OF THE CHEMICALLY COMBINED REACTION PRODUCT OF A GELATIN AND AN ALDONIC ACID, SAID REACTION PRODUCT BEING BATH SOLUBLE. 